Magnetic Field Splitting and Dispersion of the Lower 1S‐Exciton Polariton in KI and RbI

Resonances on the lower polariton branch of KI and RbI are measured by the use of three‐photon difference‐frequency generation (TP‐DFG). From these data the energy of the lowest transverse exciton state is derived. Due to the small linewidth of the resonances it is possible to measure the k‐dependent magnetic field splitting of the lower branch for the first time. The results allow to determine the exchange energy, the longitudinal‐transverse splitting and the g‐values of the uppermost valence band (Γ ‐symmetry) and the lowest conduction band (Γ ‐symmetry) with much higher accuracy than before.